Transformations of organic compounds in aqueous environments are both of considerable intrinsic interest and of great economic importance. Most of the world's fuel sources and synthetic fuel precursors have been naturally formed and modified under such conditions. The potential economic incentives for converting and upgrading organic-containing resource materials by aqueous rather than conventional hydrogen treatments is enormous. Despite the scientific and economic importance, available work on reactions of organic resource materials in water at temperatures from above about 200.degree. C. to below the critical temperature of water has been sparse and fragmentary.
The potential reserves of liquid and gaseous hydrocarbons contained in subterranean deposits are known to be substantial and form a large portion of the known energy reserves in the world. It is desirable, from an economic standpoint, to use coal and shales, for example, to produce both liquid and gaseous fuels, since both are relatively inexpensive compared to petroleum crude oil, and are quite abundant in contrast to our rapidly dwindling domestic supply of crude oil. As a result of the increasing demand for light hydrocarbon fractions, there is much interest in economical methods for recovering liquids and gases from coal and shale on a commercial scale. Various methods for recovering liquids and gases from these resources have been proposed, but the principal difficulty with these methods is that the processes are complicated and expensive, which renders the products derived therefrom too expensive to compete with products derived from petroleum crudes recovered by less expensive conventional methods.
Moreover, the value of liquids recovered from coals and shales is diminished due to the presence of high concentrations of contaminants in the recovered liquids. The chief contaminants are sulfur- and nitrogen-containing compounds which cause detrimental effects to the various catalysts utilized in these processes. These contaminants are also undesirable because of their disagreeable odor, corrosivity and undesirable combustion products.
Additionally, as a result of the increasing overall demand for light hydrocarbon fractions, there is much interest in more efficient methods for converting the heavier liquid hydrocarbon fractions recovered from coal and shale reserves into lower molecular weight materials. Conventional methods for converting these materials, such as catalytic hydrocracking, coking, thermal cracking and the like, result in the production of less desirable, high refractory materials.
During hydrocracking, hydrocarbon fractions and refractory materials are converted into lower molecular weight in the presence of hydrogen. Hydrocracking processes are more commonly employed on coal liquids, shale oils, or heavy residual or distillate oils for the production of substantial yields of low boiling saturated products and to some extent of intermediates which are utilizable as domestic fuels, and still heavier cuts which find uses as lubricants. These destructive hydrogenation processes or hydrocracking processes are operated on a strictly thermal basis or in the presence of a catalyst.
However, the application of the hydrocracking technique has in the past been fairly limited because of several interrelated problems. Conversion by hydrocracking of heavy hydrocarbon fractions recovered from coal or shale into more useful products is complicated by contaminants present in the hydrocarbon fractions. Oils extracted from coal can contain exceedingly large quantities of higher molecular weight sulfur compounds. The presence of these sulfur compounds in crude oils and various refined petroleum products and hydrocarbon fractions has long been considered undesirable. Similarly, oils produced from shales also contain undesirable nitrogen compounds in exceedingly large quantities.
For example, because of the disagreeable odor, corrosive characteristics and combustion products of sulfur- and nitrogen-containing compounds (particularly sulfur- and nitrogen-dioxide), their removal has been of constant concern to the petroleum refiner. Further, the heavier hydrocarbons are largely subjected to hydrocarbon conversion processes in which the conversion catalysts are, as a rule, highly susceptible to poisoning by sulfur and nitrogen compounds. This has, in the past, led to the selection of low-sulfur and low-nitrogen hydrocarbon fractions whenever possible. With the necessity of utilizing heavy, high sulfur and high nitrogen hydrocarbon fractions in the future, economical heteroatom removal (desulfurization and denitrogenation) processes are essential. This need is further emphasized by recent and proposed legislation which seeks to limit sulfur contents of industrial and motor fuels.
Generally, organic sulfur appears in feedstocks as mercaptans, sulfides, disulfides, or as part of complex ring compounds. The mercaptans are more reactive and are generally found in the lower boiling fractions; for example, gasoline, naphtha, kerosene, and light gas oil fractions. There are several well-known processes for sulfur removal from such lower boiling fractions. However, sulfur removal from higher boiling fractions has been a more difficult problem. Here, sulfur is present for the most part in less reactive forms as sulfides, and as part of complex ring compounds of which thiophene is a prototype. Such sulfur compounds are not susceptible to the conventional chemical treatments found satisfactory for the removal of mercaptans and are particularly difficult to remove from heavy hydrocarbon materials. Organic nitrogen appears in feedstocks as amines or nitriles or as part of complex ring compounds such as pyridines, quinolines, isoquinolines, acridines, pyrroles, indoles, carbazoles and the like. Removal of nitrogen from the more complex heterocyclic aromatic ring systems using conventional catalysts is particularly difficult.
In order to remove the sulfur and nitrogen and to convert the heavy residue into lighter more valuable products, the heavy hydrocarbon fraction is ordinarily subjected to a hydrocatalytic treatment. This is conventionally done by contacting the hydrocarbon fraction with hydrogen at an elevated temperature and pressure and in the presence of a catalyst. Unfortunately, unlike lighter distillate stocks which are substantially free from asphaltenes and metals, the additional presence of asphaltenes, which contain heavy and polar nitrogen and sulfur compounds, and metal-containing compounds, which contain heavy nitrogen species, leads to a relatively rapid reduction in the activity of the catalyst to below a practical level. The presence of these materials in the feedstock results in a reduction in catalyst activity. Eventually, the on-stream period must be interrupted, and the catalyst must be regenerated or replaced with fresh catalyst.
Aside from these technologies, conventional processes are also known to externally supply hydrogen or reducing agents to the organic resource material. In addition, these processes may also operate above the critical temperature of water or at pressures of at least 1000 psig. Conversion of organic resource materials under these conditions is known as dense fluid or gas extraction and is not the subject of applicant's inventions.
U.S. Pat. No. 3,988,238 (1976) to McCollum et al., discloses a dense-fluid extraction process for recovering liquids and gases from bituminous coal solids and desulfurizing the recovered liquids. The process is carried out in the absence of externally supplied hydrogen and the coal is contacted with a water-containing fluid at a temperature in the range of 600.degree. F. (315.degree. C.) to 900.degree. F. (485.degree. C.). However, the process requires externally supplied pressure as well as the presence of an externally supplied sulfur resistant transition metal catalyst. Applicants process does not require the presence of any externally supplied catalyst, although optionally, a catalyst may be present. However, that catalyst must be a brine or clay (i.e., layered aluminosilicates) catalyst or mixtures thereof, and is thus distinguishable from '238.
U.S. Pat. No. 4,005,005 discloses a dense fluid extraction process for recovering liquids and gases that does not require the presence of an externally supplied catalyst. It discloses and claims a reaction temperature range of 600.degree. F. (315.degree. C.) to 900.degree. F. (485.degree. C.), but all reactions were run at supercritical temperatures i.e., 710.degree. F. (377.degree. C.), which is above the critical temperature of water, 705.degree. F./375.degree. C. (reactions run below the critical temperature of water were at pressures that produce steam rather than liquid water). Most importantly, the process in '005 operates on tar sands while applicants process converts and upgrades organic resource materials selected from the group consisting of coal, shale, coal liquids, shale oils, heavy oils, and bitumens, preferably coal, shale, coal liquids, and shale oils, more preferably coal and shale, using liquid water and the corresponding autogeneous vapor pressure of the system at a temperature from about 200.degree. C. (392.0.degree. F.) to below the critical temperature of water, 374.4.degree. C. (705.degree. F.) more preferably from about 250.degree. C. to about 370.degree. C., most preferably from about 250.degree. C. to about 350.degree. C.
The above-mentioned methods do not disclose applicants process for "converting" and "upgrading" organic resource materials (as the terms are defined herein) in liquid water, in the absence of externally supplied hydrogen or other reducing agents or externally supplied catalysts, at temperatures from above about 200.degree. C. at the corresponding vapor pressure (i.e., at autogenous pressure of the system), to produce more desirable value added materials i.e., products that have lower molecular weights or increased extractability.